1. Technical Field
The present invention relates to semiconductor interconnect structures and fabrication methods, and more particularly to interconnect structures having airgaps formed therebetween using a self-aligned process.
2. Description of the Related Art
The speed of propagation of interconnect signals is an important factor controlling overall circuit speed as feature sizes are reduced, and the number of devices per unit area and the number of interconnect levels are increased. Throughout the semiconductor industry, there has been a strong drive to reduce the dielectric constant, k, of the interlayer dielectric (ILD) materials used to electrically insulate metal lines. The dielectric constant, k, of ILD materials has been steadily reduced. As a result, interconnect signals travel faster through conductors due to a reduction in resistance-capacitance (RC) delays. The ultimate dielectric constant of unity can be achieved by incorporating an airgap or vacuum as the electrically insulator between metal structures in an interconnect.
Airgap interconnects are typically formed using a mask layer over a chemical vapor deposited (CVD) interlevel dielectric (ILD) layer, patterning the mask layer, etching airgap holes and removing residual materials in the holes to form the airgaps. The patterning of these airgap structures with sub-design rule dimensions can be formed by lithographic techniques or self-assembly techniques. Both patterning processes for forming these airgaps include many opportunities for misalignment of the airgap structure over the conductive structures. Consequently, airgap interconnects thus formed suffer from reliability degradation due to these misaligned holes which form the airgap structures.